In the oil industry and particularly in the subsea field, it is common to provide arrangements that can connect and disconnect electric connections and fluid connections remotely. For instance, hydraulic connections and channels are used to control pressures and to provide mechanical movement of equipment, such as locking and unlocking of latches and valves. Furthermore, electrical connections and communication paths are provided for measurement of e.g. temperatures and pressures.
An example of such remotely (diverless or even ROV-less) established connections is the connections between a tubing hanger which is landed in the spool of a Christmas tree (XT) and the XT itself. Patent publication U.S. Pat. No. 6,158,716 describes a tubing hanger (TH) having a plurality of radially actuated coupling elements. On the radially outwardly facing side, the coupling elements have an interface adapted for engagement (i.e. abutment) with a facing counterpart arranged in the XT spool. As the TH is landed in the XT spool, the coupling elements are moved radially into engagement with the counterpart to establish sealed hydraulic couplings. The ends of hydraulic channels of the coupling elements and facing counterparts are aligned and a surrounding sealing is encircling the said facing channel ends. The appurtenant FIG. 3 is from U.S. Pat. No. 6,158,716, and shows the coupling element (20) arranged in the tubing hanger.
The sealing of the solution described in the patent publication U.S. Pat. No. 6,158,716 is established by forcing a seal carrying part (the coupling element 20) against a sealing surface (cf. sealing surface 203 of the prior art FIG. 3) of the facing part. Due to the substantial pressures which may be present in equipment associated with subsea wells, the two facing parts are forced against each other with a considerable force to ensure proper sealing. This force needs to be above a lower threshold in order to ensure the sealing function, as well as to be below an upper threshold in order to maintain the mechanical integrity of the associated parts. Hence one needs a solution which provides a pre tension between a selected upper and lower force limit.
Another goal when forcing the coupling element radially into sealing engagement with the counterpart, is to force it in a strict radial direction with the resultant force in the axial centre of the coupling element. That is, one needs to ensure that the sealing surface is forced against the facing counterpart with an even pressure throughout the area of the sealing surface.